Capt. Kristen Griest, right, and 1st Lt. Shaye Haver show off their new Ranger tabs after graduating from the Army's elite Ranger School at Fort Benning, Ga., on Aug. 21, 2015. Along with another woman, they were the first females to complete the school's grueling leadership course. (Getty Images/Jessica McGowan)

Defense Secretary Ashton Carter's announcement last December that he would open all combat positions to women in 2016 is among the most momentous military decisions since President Harry S. Truman racially integrated the armed services in 1948. Advocates of gender integration say women are fully capable of performing the difficult and sometimes brutal tasks involved with combat, and they point out that even though women have been barred officially from combat duties in Iraq and Afghanistan, female soldiers have nonetheless fought and died there. But opponents of gender integration say few women can meet the physical rigors of combat. They contend that female front-line soldiers would endanger their units and make them less lethal in battle. As the Marines, Army, Navy and Air Force move ahead to carry out Carter's order, big questions remain, including whether young women should be required, like young men, to register for the military draft.